Films amylose acetate

Schoondorp, M. A., Schouten, A. J., Hulshof, J. B. E., Feringa, B. L., and Oosteigetal, G. J. Langmuir-Blodgett Films of Amylose Acetal Dye Mixtures. 1. Monolayer Behaviour of Mixtures of Amylose Acetate and a Chiral p-Nitroazobis(benzene) Dye. Langmuir 8, 181 ... 

Physicochemical studies of other aliphatic, carboxylic esters of polysaccharides include (a) assessment of the gel-permeation properties of the series cellulose propionate-cellulose heptanoate, (b) dissolution of cellulose acetate phthalate, (c) monolayer properties of amylose acetate, and (d) melting and transition temperatures of the series amylose acetate-amylose hexanoate. Amylose acetate assumes a helical conformation at air-water interfaces and in oriented films, and the X-ray-analysis data for mannan acetate imply a threefold screw-axis... 

Starch acetates may have low or high DS. The industrial importance of low DS acetates results from their abiUty to stabilize aqueous polymer sols. Low DS acetates inhibit association of amylose polymers and reduce the association of the longer outer chains of amylopectin. These properties are important in food appHcations. Highly derivatized starches (DS 2—3) are useful because of their solubiHty in organic solvents and abiHty to form films and fibers. 

Finally, because the amylose molecule is a polyalcohol, chemical derivatives of it can be easily prepared. Included in this are the acetate, methyl, ethyl and similar derivatives, all of which belong to a class of polymers with completely different properties from the parent substance. Many of these derivatives demonstrate useful film and fiber properties, but they have not reached significant commercial utilization. All any lose derivatives crystallize easily, and many show interesting features in their crystalline state. 

Paralleling their film-forming properties, these amylose triacetates can be molded into strong, tough plastics, but the amylopectin triacetates yield only very brittle products. Similarly, Mullen and Pacsu have shown that whole starch acetate produces clear, transparent, molded pieces which, however, are brittle. 

Since amylopectin acetate produces only brittle films and plastics, its molecules probably have a non-linear structure which may be branched or coiled. A further striking difference between amylose triacetate and amylopectin triacetate is that the former can be obtained in the form of a highly fibrous mass, whereas the latter occurs only as a fine powder. 

As amylopectin predominates in all known starches, the poor film-forming properties of whole starch acetates become understandable. Artificial mixtures of amylose and amylopectin triacetates (acetylated fractions A and B) show increasingly poor film-forming properties as the proportion of amylopectin acetate in the mixture is increased. 

Starch acetates normally contain 2 to 3% moisture. They have a strong binding power for water as is indicated by the observation that an unplasticized amylose (fraction A) triacetate film soaked in water will lose about one-third of its tensile strength. 

Esters from unsaturated fatty acid chlorides are usually viscous or limpid oils soluble in hydrocarbons and turpentine, and whose primary applications are as varnishes, films, artificial threads, aqueous emulsions, and rubber-like plastics.2067,2068 Heating them in an inert gas produced insoluble products formed by polymerization involving double bonds in the acyl moieites.2069 As mentioned in the section on nitrates, acetates of amylose are less compact than amylopectin acetate.1468 Esters of unsaturated acids have also been proposed as re-moistenable adhesives.1971 1972... 

The long linear chain structure of amylose is reflected in the film-forming properties of its acetate. Films prepared from acetylated whole starch and amylopectin are quite brittle, whereas those from butanol-precipitated amylose are similar to films from high-grade cellulose acetates (94)-... 

Marchessault, Sarko etal. [10, 11] have investigated the chiroptical properties of amylose xanthates extensively. The CD of amylose triacetate in trifluoroethanol shows, apart from the expected acetyl z -> tt transition at about 230 nm, an additional shortwave peak. This is again explained by assuming a helical conformation of the amylose chain. Dextran acetates and mycodextran acetates, on the other hand, do not show conformational effects. The considerable changes in the CD spectra of amylose triacetate films when the temperature increases from 30 to 190°C are particularly remarkable. As X-ray diffraction analysis shows, these effects are connected with crystallisation processes and transformation during annealing. 

The products 41 and 42 were insoluble in any solvents, e.g., aqueous acetic acid and DMSO, which were good solvents for chitosan and amylose, respectively. The XRD patterns of these materials showed typical A-type crystalline structures due to amyloses. Such crystalline structures are generally attributed to the formation of a double helix of amylose [33]. Therefore, we assume that one of the reasons for the insolubility of these materials is probably caused by molecular aggregation as a result of this crystalline structure. The aggregation in the material would contribute its conversion into film and hydrogel forms. For example, the hydrogel of 41 could be formed by drying the reaction mixture slowly in the vessel at 40-50 C. 

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